The invention relates to an apparatus for pulling monocrystals out of a melt situated in a crucible under vacuum. The apparatus has a vacuum chamber in which the crucible is disposed, a means for heating the melt, a pulling means above the melt, and a cover having an opening and situated above the melt through which the monocrystal can be pulled upwardly from the surface of the melt.
When monocrystals are pulled from a melt under vacuum conditions it is very important to keep the temperature ratios at the crucible margin as low as possible and prevent flows from forming in the melt.
To counteract disadvantageous effects in the pulling of monocrystals in a known apparatus for pulling monocrystals (U.S. Pat. No. 3,359,077 to Arst) a cover has already been used over the melt to reduce the thermal gradient at the surface of the melt.
It is furthermore known (EU-0 170 856) to make the crucible for the melt bipartite and provide it with a cylindrical insert and arrange the charging funnel of a recharging apparatus such that the recharging material can be poured into a marginal portion remaining between the margin of the inner shell of the crucible and the insert. This known apparatus is equipped with two heaters of which one has a flat, discoidal configuration and is held underneath the crucible, and the other is in the form of a hollow cylindrical body surrounding the crucible.
Lastly, an apparatus (U.S. Pat. No. 3,511,610) is already known which serves to reduce any excessively great temperature difference between the end of the seed crystal and the melt, the part bearing the seed crystal being provided with a heating means by which the heat can be transferred to the seed crystal with the aid of the carrier of the latter. This purpose is served by a plate on the element that pulls up the crystal holder.